1. Field of the Invention
Modern injection systems for injecting fuel into the combustion chambers of air-compressing internal combustion engines use high-pressure accumulators (common rails). These high-pressure accumulators, which are usually tubular and constructed with thick walls, have throttle valves located at pressure tube connections. The throttle valves damp the reflected pressure waves that can be generated when the nozzle in the fuel injector closes at the end of the injection process.
2. Prior Art
DE 196 50 865 A1 discloses a solenoid valve for controlling the fuel pressure in the control pressure chamber of an injection valve, for example in the injector of a common rail injection system. The fuel pressure in the control pressure chamber is used to control the movement of a valve piston that opens and closes an injection opening of the injection valve. The solenoid valve has an electromagnet contained in a housing part, a movable armature, and a control valve element; this control valve element is moved by the armature, is acted on in the closing direction by a closing spring, and cooperates with a valve seat of the solenoid valve, thus controlling the flow of fuel out of the control pressure chamber. The relief of pressure in the control chamber causes the nozzle needle inside the injector body to move in the opening direction, whereas an exertion of pressure on the control pressure chamber produces a closing movement of the nozzle needle, which closing motion is the source of the pressure pulsations, i.e. the reflected pressure waves.
DE 197 08 104 A1 also discloses a solenoid valve for controlling the fuel pressure in the control pressure chamber of an injection valve. This valve is likewise used in the injector of a common rail injection system. The solenoid valve has an electromagnet contained in a housing part, a movable armature, and a control valve element that is moved by the armature; this control valve element is acted on in the closing direction by a closing spring, and cooperates with a valve seat of the solenoid valve, thus controlling the flow of fuel out of the control pressure chamber. According to the embodiment disclosed in DE 197 08 104 A1, the armature of the solenoid valve is comprised of two parts, with an armature bolt and an armature plate that is supported so that it can slide smoothly on the armature bolt. The two-part design reduces the effective mass to be decelerated and therefore reduces the chattering behavior of the armature. However, the armature plate that can be moved in relation to the armature bolt can continue to oscillate on the armature bolt in a disadvantageous manner after the closing of the solenoid valve, and can thus trigger the occurrence of pressure pulsations, i.e. reflected pressure waves when the injection valve element closes.
The Bosch Manual “Diesel Motor Management”, 2nd updated and expanded edition; Vieweg 1998, Braunschweig/Wiesbaden ISBN 3-528-03873-X, p. 231, right column, describes a return flow throttle valve, which is used to damp pressure waves in fuel injection systems. The return flow throttle valve known from the above-cited literature prevents the pressure waves generated at the end of the injection process and their reflections from causing a reopening of the nozzle needle, i.e. of the injection valve element. An uncontrolled reopening of the nozzle needle and the resulting secondary injection into the combustion chambers of the engine would have very negative repercussions on the emissions in the exhaust of the air-compressing internal combustion engine since the percentage of uncombusted hydrocarbons would rise considerably with the occurrence of uncontrolled secondary injections.
At the onset of fuel delivery, the spring-loaded valve cone of the return flow throttle valve is lifted away from its seat by the fuel pressure. The fuel is then conveyed to the injection nozzle via a pressure tube connection and the pressure tube line. At the end of the fuel delivery, the fuel pressure drops abruptly. The valve spring presses the valve cone back against the valve seat. During the closing of the injection nozzle, a throttle restriction incorporated into the valve cone reduces reflected pressure waves in the fuel injector to such an extent that it prevents damaging pressure wave reflections that would contribute to a premature fatiguing of the material of the high-pressure accumulator.
In the known return flow throttle valve, it is disadvantageous that the return flow throttle elements take up a relatively large amount of space. This has a negative impact on installation possibilities; moreover, there is only a very limited amount of space available in the cylinder head region of internal combustion engines. Furthermore, embodying the return flow throttle as a multi-part component has a negative impact on the number of sealing points.